1. Technical Field
The present disclosure relates to a variable-flow-rate valve mechanism and the like, which opens and closes an aperture of a variable-flow-rate gas passage in order to adjust a flow rate of an exhaust gas to be supplied to a turbine wheel side in a turbocharger such as a vehicle turbocharger.
2. Description of the Related Art
In a turbine housing of a vehicle turbocharger, a bypass passage for causing part of an exhaust gas to bypass a turbine wheel is usually formed as a countermeasure for suppressing an excessive rise in boost pressure by the vehicle turbocharger. Moreover, a waste gate valve configured to open and close an aperture (an aperture on an outlet side) of the bypass passage is provided at an appropriate position of the turbine housing. Here, the bypass passage is one of variable-flow-rate gas passages configured to adjust a flow rate of the exhaust gas to be supplied to the turbine wheel side, while the waste gate valve is one of variable-flow-rate valve mechanisms configured to open and close the aperture of the variable-flow-rate gas passage. Here, a general configuration and the like of the waste gate valve being one of the variable-flow-rate valve mechanisms are as follows.
A support hole is penetratingly formed in an outer wall portion of the turbine housing. A stem (a rotating shaft) is supported in this support hole in such a way as to be rotatable in forward and reverse directions. A base end portion (one end portion) of the stem projects outward from the outer wall portion of the turbine housing. A base end portion (one end portion) of a link member is integrally connected to the base end portion of the stem. The link member is driven by an actuator to swing in the forward and reverse directions around a shaft center of the stein.
A base end portion of an attachment member is integrally connected to a leading end portion (another end portion) of the stem. An attachment hole is penetratingly formed in a leading end portion of the attachment member. Moreover, a valve is fitted into the attachment hole of the attachment member. The valve allows for play (inclusive of tilt and slight movement) with the attachment member. The valve includes: a valve body (a valve body portion) provided with a valve surface capable of coming into and out of contact with a valve seat on the periphery of the aperture of the bypass passage; and a valve shaft serving as a valve connecting member (a valve connecting portion), which is integrally provided to a head portion (on the opposite side from the valve surface) of the valve body and is fitted into and connected to the attachment hole of the attachment member. A stopping member (a stopper) for preventing detachment of the valve from the attachment member is integrally provided to a leading end portion of the valve shaft.
Here, when the boost pressure reaches a preset pressure, the link member is driven by the actuator to swing in the forward direction. Thus, the valve swings in the forward direction (an opening direction) through the stem and the attachment member, thereby opening the aperture of the bypass passage. When the boost pressure falls below the preset pressure after the aperture of the bypass passage is opened, the link member is driven by the actuator to swing in the reverse direction. Thus, the valve swings in the reverse direction (a closing direction) through the stem and the like, thereby closing the aperture of the bypass passage. By allowing for play (backlash) between the attachment member and the valve, the valve surface of the valve body has better fitting performance to (better contact with) the valve seat in closing the aperture of the bypass passage, thereby securing operation stability (reliability) of the waste gate valve.
Related techniques are illustrated in Japanese Patent Application Publication No. 2013-155687 (Patent Literature 1), Japanese Patent Application Publication No. 2009-236088 (Patent Literature 2), and Japanese Patent Application Publication No. 2008-101589 (Patent Literature 3).